Polymers having reactive silicon groups cure by formation of crosslinks in the presence of moisture. Among these polymers, curable compositions containing polymers having polyoxypropylene main chain skeletons are liquid at room temperature and cure into materials having rubber elasticity. Thus, they are widely used as building sealants (refer to patent document 1 and patent document 2 below).
Among various requirements and demands for curable compositions for building applications, dynamic durability is important for sealants for working joint applications.
In the United States, silicone sealants are well known as durable sealants. The durability of the silicone sealants is classified as CLASS 100/50 according to the standard of American Society for Testing and Materials (ASTM) C920, wherein 100 denotes 100% elongation and 50 denotes 50% compression. The classification, “CLASS 100/50” is the highest rating given for dynamic durability. No sealant is recognized as being highly durable sealants unless the sealant has sufficient performance that passes this durability test.
The durability test for ASTM C920 is carried out according to a test method set forth in ASTM C719, the Hockman cycle. According to an established theory of material designing, materials other than silicone rarely achieve the required high recovery ratio.
Curable compositions containing polymers having reactive silicon groups and polyoxypropylene main chain skeletons have sufficient sealant properties such as workability and adhesiveness; however, they have lower recovery ratios compared to that of silicone sealants. Thus, such compositions have been considered difficult to pass the CLASS 100/50 dynamic fatigue testing according to ASTM C719. Furthermore, attempts have been made to search for compositions that can pass CLASS 100/50 dynamic fatigue testing, but no such technique has been found so far.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 5-125272    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 3-072527